In episode 8 of “Old Enough!” on Netflix at 2:45 the mother has one and I also saw one that Seiko Matsuda and her husband carried after their daughter passed.
https://www.reddit.com/r/japan/comments/vhlg3z/what_are_the_wrapped_boxes_called_that_are_used/
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That would be a kotsubako. It contains the funeral urn, that contains the ashes, prior to it being interned. Usually an indicator of a recent death since the box is discarded after the urn in interned, although there can be circumstances where a person may need to keep the urn at home for extended periods of time
Dictionary entry: https://jlearn.net/dictionary/骨箱